RL11 disk controller

From Computer History Wiki
Revision as of 00:18, 9 January 2022 by Jnc (talk | contribs) (clarify)
Jump to: navigation, search
RL11 M7762 card

The RL11 disk controllers (the original RL11 for the UNIBUS, and the RLV11 and RLV12 for the QBUS) were for the RL01 and RL02 disk drives. (These drives protect the data, and sector headers, with separate CRCs.)

The RL11 was a hex board, the M7762. The RLV11 consisted of two quad boards, the M8013 and M8014, which used the CD interconnect to communicate; it was program compatible with the RL11. The RLV12 was a single quad board, the M8061; it was mostly program compatible, but added a 'Bus Address Extension' register for use on Q22 systems.

All have a 40-pin Berg connector header holding a flat cable, which runs to a bulkhead-mounted converter from the flat cable to a special inter-drive cable (round in cross-section, with special locking connectors). (If the flat cable is plugged in the wrong way around, nothing is damaged; the drive merely turns on its 'fault' light.)

The cable runs from the converter to the first drive; up to 4 drives can be connected to a single controller, using a bus running from one drive to the next, with a terminator in the last drive of the string.

Controller capabilities

RLV12 card

The controller and drive combination can execute 8 different commands:

  • No Operation
  • Write Check
  • Get Status
  • Seek
  • Read Header
  • Write Data
  • Read Data
  • Read Data Without Header Check

Implied seeks (i.e. setting the disk address, and then starting a read or write operation, which is intended to happen at that address) are not supported; an explicit seek to the desired cylinder must be performed before the read or write. (This is in part because the Disk Address register is shared between the cylinder move number, during a seek operation, and the starting sector number, during a read or write operation.) Spiral reads and writes (i.e. multi-block reads which start on one track, and overflow to the next) are also not supported; multiple separate read/write commands are needed, with a seek to the next track between each pair.

Device registers

The RL11 controller includes 4 (5 for the RLV12) read-write registers:

Register Abbreviation Address
Control Status Register RLCS 774400
Bus Address Register RLBA 774402
Disk Address Register RLDA 774404
Multipurpose Register RLMP 774406
Bus Address Extension Register
RLV12 only 		RLBAE 774410

774400: Control Status Register (RLCS)

CERR DE NXM DLT/HNF DCRC/ HCRC OPI DRVSEL CRDY IE BUS ADDR EX FUNC DRDY
15 14 13 12 11 10 09 08 07 06 05 04 03 02 01 00
Function Code Function
0 No Operation
1 Write Check
2 Get Status
3 Seek
4 Read Header
5 Write Data
6 Read Data
7 Read Data, No Header Check 
OPI - Operation Incomplete
DCRC/HCRC/WCE - Data CRC/Header CRC/Write Check Error
DLT/HNF - Data Late / Header Not Found
DE - Drive Error ('Get Status' will provide details)
CERR - Composite Error

774402: Bus Address Register (RLBA)

BA15 <---> BA01 0
15 14 13 12 11 10 09 08 07 06 05 04 03 02 01 00

774404: Disk Address Register (RLDA)

During a 'Seek' command on an RL01:

0 CYL ADDR DIFF Reserved HD SEL 0 DIR 0 1
15 14 13 12 11 10 09 08 07 06 05 04 03 02 01 00

During a 'Seek' command on an RL02:

CYL ADDR DIFF Reserved HD SEL 0 DIR 0 1
15 14 13 12 11 10 09 08 07 06 05 04 03 02 01 00

During a 'Read Data' or 'Write Data' command on an RL01:

0 CYL ADDR HD SEL SECTOR
15 14 13 12 11 10 09 08 07 06 05 04 03 02 01 00

During a 'Read Data' or 'Write Data' command on an RL02:

CYL ADDR HD SEL SECTOR
15 14 13 12 11 10 09 08 07 06 05 04 03 02 01 00

During a 'Get Status' command:

Unused MBZ RESET 0 GT STA 1
15 14 13 12 11 10 09 08 07 06 05 04 03 02 01 00

774406: Multipurpose Register (RLMP)

During a 'Read Data' or 'Write Data' command:

111 WORD COUNT
15 14 13 12 11 10 09 08 07 06 05 04 03 02 01 00

During a 'Get Status' command:

WDE CHE WL SKTO SPE WGE VC DSE Rsvd HS CO HO BH STATE
15 14 13 12 11 10 09 08 07 06 05 04 03 02 01 00
State Code State
0 Load Cartridge
1 Spin Up
2 Brush Cycle
3 Load Heads
4 Seek
5 Lock On
6 Unload Heads
7 Spin Down

During a 'Read Header' command, three successive reads to the Multipurpose Register will return in the first word, on an RL01:

0 CYL ADDR HD SEL SECTOR
15 14 13 12 11 10 09 08 07 06 05 04 03 02 01 00

and on an RL02:

CYL ADDR HD SEL SECTOR
15 14 13 12 11 10 09 08 07 06 05 04 03 02 01 00

followed by all 0's in the second word, and the header CRC in the third.

774410: Bus Address Extension Register (RLBAE)

Unused BA21 <---> BA16
15 14 13 12 11 10 09 08 07 06 05 04 03 02 01 00

Note: This register is present in the RLV12 only.

Bootstraps

This bootstrap (which is position-independent object code, so it can be placed anywhere; 04000 is good) will load the block at sector 0 of cylinder 0 of drive 0 into main memory at address 0:

Address Data Mnemonic Description
1000 012700 MOV #174400,R0 Move the address of the Control Status register into R0
1002 174400 (constant)
1004 012760 MOV #177400,6(R0) Move block size (negative) into Multipurpose register
1006 177400 (constant)
1010 000006 (constant)
1012 012710 MOV #14,@R0 Move 'Read Go' command into CSR
1014 000014 (constant)
1016 105710 TSTB (R0) Test for 'Done' bit in CSR
1020 100376 BPL 1016 Jump backward if not set
1022 005007 CLR PC Start loaded bootstrap with jump to 0

Note that the INIT pulse caused by hitting the front panel's 'Start' button will clear the Bus Address register, so that the loaded block will be placed at location 0; and the Disk Address register, so that sector 0 will be read. If the drive's heads are not on cylinder 0, since a seek on an RL01/02 is relative, a 'Read Header' command would have to be done before a seek could be commanded (or the device driver must remember the current cylinder), and that all would require a fair amount of code. To ensure that the drive is on cylinder 0 for the bootstrap, the drive should be power cycled before starting the bootstrap.

External links

Retrieved from "https://gunkies.org/w/index.php?title=RL11_disk_controller&oldid=24994"